The present invention relates to the field of transporting viscous fluids such as extra heavy crude oils, bitumen or tar sands which hereinafter will be referred to as viscous oils.
Friction losses are often encountered during the pumping of viscous fluids through a pipeline. These losses are due to the shear stresses between the pipe wall and the fluid being transported. When these friction losses are great, significant pressure drops occur along the pipeline. In extreme situations, the viscous fluid being transported can stick to the pipe walls, particularly at sites which are sharp changes in the flow direction.
A known procedure for reducing friction losses within the pipeline is the introduction of a less viscous immiscible fluid such as water into the flow to act as a lubricating layer for absorbing the shear stress existing between the walls of the pipe and the fluid. This procedure is known as core flow because of the formation of a stable core of the more viscous fluid, i.e. the viscous oil, and a surrounding, generally annular, layer of less viscous fluid. U.S. Pat. Nos. 2,821,205 to Chilton et al. and 3,977,469 to Broussard et al. illustrate the use of core flow during the pipeline transmission of oil.
Normally, core flow is established by injecting the less viscous fluid around the more viscous fluid being pumped in the pipeline. U.S. Pat. Nos. 3,502,103 and 3,826,279, both to Verschuur, and 3,886,972 to Scott et al. illustrate some of the devices used to create core flow within a pipeline. An alternative approach for establishing core flow is illustrated in U.S. Pat. No. 4,047,539 to Kruka wherein the core flow is created by subjecting a water-in-oil emulsion to a high shear rate.
Although fresh water is the most common fluid used as the less viscous component of the core flow, other fluids or a combination of water with additives have been used. U.S. Pat. No. 3,892,252 to Poettman illustrates a method for increasing the flow capacity of a pipeline used to transport fluids by introducing a micellar system into the fluid flow using a hollow pig. The micellar system comprises a surfactant, water and a hydrocarbon. The hollow pig exudes the micellar system onto the walls of the pipe as it is carried downstream by the transport fluid.
U.S.S.R. Pat. No. 485,277 to Avdshiev illustrates a core flow method which uses a lower viscosity fluid formed by an emulsion of a light fraction of hydrocarbon in water. U.S.S.R. Pat. No. 767,451 to Budina et al. illustrates a core flow method wherein the lower viscosity fluid is a solution of water and synthetic tensoactive agents.
While extensive experimental and analytical studies have been carried out to demonstrate that core-annular flow is a feasible method for the transport of heavy and extra-heavy crude oils and bitumen at ambient temperatures, little, if any, attention has been given to the manner in which this flow pattern is to be established in a commercial pipeline. The effectiveness of the commercial use of core flow is related to its adaptability to existing pipeline systems. It is then clear that core-flowing viscous oils involves not only basic technical questions but also operational methodologies aimed at increasing the flexibility of the method. In particular, pipeliners should be able to utilize core-flow in existing pipelines which, in turn, implies that its use involves the sharing of the pipeline with other types of fluids that are not core-flowed. This latter requirement places a severe constraint to the use of core-flow, since the standard method for establishing it requires a multi-step process consisting of the following. First, the entire pipeline is emptied. Second, it is filled with water. Finally, the water is displaced by the viscous oil which as it moves through the line forms the core-flow pattern.
Accordingly, it is an object of the present invention to provide a new process for establishing core-flow in commercial pipeline systems.
It is a further object of the present invention to provide a process as above which does not require the pipeline to be emptied.
It is yet a further object of the present invention to provide a process as above which allows the batching of core-flow transported viscous oil with other fluids.
These and other objects and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements.